Because of the redundancy and error checking built into the CD format, occasional missing or corrupt bits can easily be detected and corrected. As the track is circular, scratches in a circular direction are more likely to damage contiguous bits and therefore make recovery of the information more difficult.
That is to say, in the case of a scratch running from the centre to the edge of the disk, any damaged bits will be much further apart and less likely to be related.
Just as a BTW, my friend's husband got a new car, and while he was out, his teen aged daughter decide to clean it for him, which she did with a kitchen scourer. It required a total respray...
I'm pretty sure also that there was a question in motoring quite recently from someone who'd done a similar thing.
Yes, but I always clean radially because there's always a chance that you could get a bit of grot on the cloth (or there might already be some on the CD, which you will end up dragging with the cloth) - why take the risk?